If you cast Genesis Ultimatum and that gets you a card with mutation and you already have a non-mutated creature on the board, despite not being able to play the mutated creature, it still asks you if you want to play it as a mutation or not. It doesn’t matter what you answer since it won’t play it anyway. It shouldn’t be asking the question.
This issue is now under investigation.
Thank you for the feedback,
Marcela.